The present invention relates to internal mold release systems which may be used in the preparation of reaction injected polyurethanes and polyurea foam articles. These internal mold release systems are particularly useful in manufacturing shaped resin components by the structural reaction injection molding (SRIM) process, wherein a liquid stream of polyisocyanate is impingement mixed with at least one other stream containing active hydrogen-containing liquids and optionally, catalysts, fillers, mold release systems, etc., and transferred to a heated metal mold. A glass mat or a mat of other structural fibers is placed into the mold prior to the impingement mixing of the components so that the final product is a reinforced composite. SRIM processes are used commercially to manufacture various articles where high strength and low weight are of importance. For example, SRIM processes are used to manufacture interior trim substrates for automobiles, such as door panels, package trays, speaker enclosures and seat pans.
Developments in the chemistry of the polymer systems used in SRIM processes have resulted in urethane and urethane-urea polymers which are sufficiently cured to be demolded within about 50-90 seconds after injection. SRIM equipment has also improved so that the mechanics of opening and closing the mold also require only about 40-70 seconds. Urethane polymers, being excellent adhesives, bond tenaciously to metal making it necessary to utilize a release agent so that parts can be quickly and easily removed from the mold without damage or distortion.
External mold release agents are used by applying the release agent directly to the surfaces of the mold. The mold must be completely covered with the release agent, generally by spraying a solution or an emulsion of a soap or wax onto the surface of the mold. This procedure requires a minimum of 30-60 seconds and must be repeated at least after every one to five parts, thus increasing the part to part cycle time by as much as 50%. Additionally, this constant spraying often causes excessive mold release agent to build up on areas surrounding the mold surface or on the mold surface itself. In this instance, the mold must be periodically wiped off and/or cleaned by solvent or detergent wash which is both time consuming and costly for the part manufacturer.
Thus, it is clear that mold release agents or systems which may be contained in the reaction systems themselves, i.e., internal mold release agents or systems, would be advantageous in eliminating such difficulties, increasing productivity and reducing part cost. Various internal mold release agents have been proposed in an attempt to solve these problems. For example, U.S. Pat. Nos. 4,546,154 discloses the use of 0.5-1.5 percent by weight of polysiloxane mold release agents in reaction injection molding systems for this purpose. However, such materials have been found to provide an insufficient number of releases to make their use commercially acceptable.
Certain acids, such as fatty acids and their esters, are known to act as mold release agents. For example, U.S. Pat. No. 4,098,731 discloses the use of salts of saturated or unsaturated aliphatic or cycloaliphatic carboxylic acids containing at least eight carbon atoms and tertiary amines which do not contain amide or ester groups as release agents for polyurethane foam production. U.S. Pat. No. 4,024,090 discloses the use of internal mold release agents which are the esterification reaction products of polysiloxanes and monocarboxylic or polycarboxylic acids. U.S. Pat. Nos. 5,128,807, 4,058,492, 3,993,606 and 3,726,952 all also disclose the use of carboxylic acids or their derivatives as mold release agents. U.S. Pat. No. 4,130,698 discloses the use of esters of a fatty acid, such as glycerol trioleate, olive oil and peanut oil, as a processing aid. However, such systems have proven to be disadvantageous as they provide a relatively minor improvement in release performance, particularly in SRIM systems.
Other materials have been used to provide a release effect in molding operations. For example, U.S. Pat. No. 3,875,069 discloses lubricant compositions useful in shaping thermoplastic material comprising: (A) mixed esters of (a) aliphatic, cycloaliphatic and/or aromatic dicarboxylic acids, (b) aliphatic polyols and (c) aliphatic monocarboxylic acids with (B) esters of (1) dicarboxylic acids and long chained aliphatic monofunctional alcohols (2) long chained aliphatic monofunctional alcohols and long-chained monocarboxylic acids and (3) full or partial esters of aliphatic polyols and long-chained aliphatic monocarboxylic acids. U.S. Pat. No. 5,389,696 discloses a process for producing a molded foam part using an internal mold release agent which comprises (a) 1-10% of mixed esters comprising the reaction product of i) aliphatic dicarboxylic acids, ii) aliphatic polyols, and iii) monocarboxylic acids. This patent specifically excludes the esters of the U.S. Pat. No. 3,875,069. However, as with other internal release agents, the release materials disclosed in these patents have not demonstrated the ability to provide consistently good results.